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How much psi of compression should a 1989 - 225 have? Also at what psi is the minimum? I don't want to buy a motor that is ready for a rebuild. The guy told me the engine runs great and pushes his 20' mako around 60 mph. I've never been in a boat with a single screw that would do 60 mph. Is this guy full of crap? Thank you in advance for any replies.
Dennis
 

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More important than the actual compression reading is having even or near even numbers across all six cylinders on that motor. Compression will drop a bit with hours and age.

I owned a 1974 20' Mako CC that I dropped a 1998 Evinrude Ocean Pro on her brand new back in '98. That boat ran 50MPH, so I can imagine a 225HP(overpowered) pushing it even faster.
 

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Don't know about an 89 but I have a 99 ox-66 and it was 120 for all but the bottom which were 115. The two lower cylinders have less compression due to combustion chamber volume changed for smoother operation when the 2 cylinder's shut down under 1900 RPM.
 

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Hey Menace, depending on the hours and its care over the years anywhere from 85 to 110 would be ideal. More importantly is what Adam said, even compression within 5 to 10psi across cylinders. The top cylinders tend to have less compression due to them running hotter than the lower cylinders. Another thing to check is the shift shaft.It should be stainless steel,some were not, and to change you need to remove the power head which on an 89 is gonna be a dog due to the corrosion. You can see the top part of the shaft if you look by the steering arm. Other than that those were good motors-good luck
 

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I had a 1990 20' Hydra Sport with a 1997 175 HP Johnson Ocean Runner that would hit 50 MPH (so maybe 60 MPH with a 225 is possible)
 

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You will not find published compression specs on most motors. There are way to many variables ,temperature, air density, guage calibration, cranking speed and the list goes on. What you are looking for is a 10 percent maximum variance between cylinders. You need to be cautious, I have seen situations where a bad cylinder has actually read higher due to excessive carbon build up around the rings. It is always best to have someone with a bore scope to look in each cylinder.
 

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Compression of a v6 yam??

I have a 99 250 ox66 that runs and starts better than any past motor I have ever owned! Now for the compression lower port cyl 86 psi the other 5 aprox. 100 psi. ? I repeat it runs and starts so good that I had a second comp. test to verify? I had planned to rebuild it last spring but instead I fished it offshore at hatteras than striper fished the sandbars of great egg inlet till late dec. It always started on a half of a crank. even in breakers.should I rebuild?????
 
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